The specific aims of this investigation are: i. To study by transductional analysis the extracellular proteins and surface antigens thought to be associated with the virulence of S. aureus in an effort to assess their role in both the infectious process and the metabolism of the organism. ii. To analyze by tranduction the determinants of resistance to chemotherapeutic agents to learn more about the mechanism of emergency of resistant strains in native. iii. To study the possible role of interspecific transduction between S. aureus and S. epidermidis in the emergence of virulent or resistant strains of each species. iv. To map by transductional procedures the chromosome of S. aureus.